Alkoxysilane compounds are widely known and available and are used in either solvent based or aqueous based coating compositions. In solvent based compositions the silane compound or a polymer containing silane is dissolved in a hydrophobic organic solvent or alcohol. Although this composition is very efficient, it suffers drawbacks, such as toxicity or a harmful influence on environment. These drawbacks are substantially reduced with the use of aqueous based coatings, but these aqueous based coatings can exhibit reduced waterproof properties. The aqueous based compositions are mainly ordinary emulsion polymers containing alkoxysilane that are prepared in the presence of a surfactant and a polymerization initiator, or they are hydrophobic resins containing silane that are compulsorily emulsified in the presence of water-soluble high molecular weight molecules. These surfactants, water-soluble polymerization initiators, and water-soluble high molecular weight molecules utilized in the polymerization process can persist in the films formed from the emulsion polymers and cause a reduction in waterproofing properties. Furthermore, the alkoxysilane compound itself is subject to hydrolysis and condensation, which during the polymerization process can cause gelation and a deterioration in the stability of the polymerization through anastomosis of the emulsion particle. For these reasons alkoxysilane compounds have not previously been put into practical use in aqueous based coating materials.
Accordingly, an object of the invention is to provide aqueous coating compositions that can form a paint film with excellent waterproof properties and adhesion to various substrates.